This file is almost 200mb for me, I assume this is for caching custom emojis? In that case it is safe to delete the file to make up space?

As a possible legitimate feature request instead of a question, make the file autotrim/delete when too large, discord_avatars is only 57mb for example

Yes, it's safe to delete. There's no auto-trim function yet, since there's no easy way to know when it's a good time to do so, and which things to trim.